Oakland police officers interview people near the scene of a fatal shooting involving a fellow officer on Thursday.
Photograph: Ben Margot/AP

Three police killings within a day in California have sparked a quick response from activists in California and across the country demanding thorough investigations into the three separate incidents.

In Oakland, residents are questioning the response from an 18-year police veteran who shot and killed a man on Thursday morning after he allegedly was swinging a metal bike chain. Later on Thursday, officers with the Los Angeles police department shot and killed a 30-year-old man following a dispute with neighbors. And in the early hours of Friday morning, San Diego police killed a 54-year-old man who was allegedly moving in the officer’s direction with a box cutter before being gunned down.

All three police departments have defended their officers’ actions.

Oakland police chief Sean Whent said at a press conference that “the suspect continued to advance, swinging the chain at the officer. The officer drew her firearm and fired at the suspect, striking him.”

The Oakland incident, at MacArthur Boulevard and Van Buren Avenue, is the sixth such police shooting this year and the fourth fatality in the city. According to Whent, the officer was recovering at a local hospital from injuries reportedly sustained in the incident. The body-camera footage from the incident has not been released.

“I don’t think what he did was worth his life being taken, just by knowing him personally,” local resident Rebecca Ellis told KGO-TV Channel 7.

A protest against police violence in Oakland and across the country was held Thursday late afternoon and again stirred concerns in the Bay Area city that unrest is fomenting.

In Los Angeles, the police shooting was the 28th of the year and 14th fatality thus far. According to police accounts, LAPD officers arrived in Van Nuys shortly before midnight. Sergeant Barry Montgomery said that after the officers arrived “a physical altercation ensued”.

The officers said the man “attacked” them before he was shot and killed. The officers were taken to hospital for minor injuries.

A resident from the area told local NBC-4 that the man killed was most likely a squatter who had taken up shop in the home where he was shot dead. Police could not corroborate the situation surrounding how the man found his way to the house. LAPD did not reply to requests for comment.

In San Diego, police shot a man outside a drug store when responding to a complaint that the man, 54 and allegedly armed with a box cutter, was threatening employees.

The unnamed officer, a 15-year-veteran, warned the man.

“The suspect ignored those commands and quickly advanced on the officer, while holding the blade pointed at the officer,” San Diego police homicide lieutenant Mike Hastings told the Union-Tribune. The officer in that incident was wearing a body camera, the paper reported.

Police violence has become a major political and social issue in the US over the past year, with activists across the country demanding justice for those affected by police violence and greater accountability for police.